Thermoplastic elastomers do not require a vulcanization process and can be processed by a molding machine for processing an ordinary thermoplastic resin. These characteristics are being harnessed to use thermoplastic elastomers in a broad range of fields, including automobile parts, home electric appliances or other miscellaneous goods. Among thermoplastic elastomers, an olefinic thermoplastic elastomer obtained by kneading an olefin copolymer rubber obtained by polymerizing ethylene, an α-olefin having 3 to 20 carbon atoms and a non-conjugated polyene, with an olefin resin, is widely used as a material that is light weight, recyclable, chlorine-free and environmentally friendly.
Known production methods of olefinic thermoplastic elastomers include kneading an olefin copolymer rubber and an olefin resin in a closed mixer as exemplified by a Banbury mixer. However, because a batch kneader, such as a Banbury mixer, is used, this method suffers from the problems of having poor productivity and being inefficient.
A method known for resolving these problems is to knead the olefin copolymer rubber and olefin resin with a twin-screw extruder. For example, JP-A-5-220825 describes a method for producing an olefinic thermoplastic elastomer composition by directly supplying a mixture mainly composed of an olefin copolymer rubber and a polyolefin resin to a twin-screw extruder with a L/D of 20 or more, during a dynamic heat treatment in the presence of an organic peroxide having a temperature of 160° C. or more, which half-life is one minute; controlling the cylinder temperature at the raw material supply port side of the twin-screw extruder to between 130 to 155° C. over a length ten times that of the port diameter of the twin-screw extruder; and controlling the cylinder temperature at the die side, excluding the cylinder portion which is controlled at the temperature at between 180 to 280° C., over a length ten times that of the port diameter of the twin-screw extruder.